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            <h1 style="display: none">14.观察者模式</h1>
            
            
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                <h1 id="观察者模式"><a href="#观察者模式" class="headerlink" title="观察者模式"></a>观察者模式</h1><p>观察者模式的应用场景非常广泛，小到代码层面的解耦，大到架构层面的系统解耦，再或者一些产品的设计思路。</p>
<p>我们常说的基于事件驱动的架构，其实也是观察者模式的一种最佳实践，当我们观察摸一个对象时，对象传递出的每一个行为都被看成是一个事件，观察者通过处理每一个事件来完成自身的操作处理。</p>
<h2 id="概念"><a href="#概念" class="headerlink" title="概念"></a>概念</h2><p>定义对象之间的一对多依赖关系，这样当一个对象改变时，他的<strong>所有依赖项都会自动得到通知更新</strong>。</p>
<p>在观察者模式中发生变化的对象成为观察目标，而被通知的对象成为观察者，一个观察目标可以应对多个观察者，而且这些观察者之间可以没有任何相互关系，可以根据自己的需求增加和删除观察者。</p>
<p>别名： 发布订阅者模式。</p>
<h2 id="结构"><a href="#结构" class="headerlink" title="结构"></a>结构</h2><p>红路灯模式为例介绍</p>
<ol>
<li>抽象被观察者(Subject): 定义了被观察者的方法，并实现了消息的订阅添加和发送通知&lt;或者在具体观察者中实现&gt;； 添加车和人的消息订阅，并将红灯还是绿灯展示给人和车</li>
<li>具体被观察者(ConcreteSubject): 实现具体业务，只是先期的变化业务，不需要关心通知业务。</li>
<li>抽象观察者(Observer): 声明 doEvent 方法</li>
<li>具体观察者(ConcreteObserver): 实现接收到信号后需要执行的业务。</li>
</ol>
<h2 id="应用场景"><a href="#应用场景" class="headerlink" title="应用场景"></a>应用场景</h2><ol>
<li>当一个对象状态的改变需要改变其他对象时。比如：商品库存数量发生变化时，需要通知商品详情页、购物车等系统改变数量。</li>
<li>当一个对象发生改变时只想要发送通知，而不是需要知道接受者是谁。比如：订阅微信公众号的文章，发送者通过公众号发送，订阅者并不知道哪些用户订阅了公众号。</li>
<li>需要创建一种链式触发机制时。 比如：在系统中创建一个触发链，A对象的行为将影响B对象，B对象的行为将影响C对象，这样通过观察者模式能够很好的实现。</li>
<li>微博或朋友圈发送的场景。这观察者模式的典型应用场景，一个人发微博或朋友圈，只要是关联的朋友都会收到通知；一旦取消关注，此人以后将不会收到相关通知。</li>
<li>需要建立基于事件触发的场景。比如： 基于Java UI 的编程，所有键盘和鼠标事件都是由它的侦听器对象和指定函数处理，当用户点击鼠标时，订阅鼠标单击事件的函数将被调用，并将上下问数据作为方法参数传递给他。</li>
</ol>
<h2 id="优点"><a href="#优点" class="headerlink" title="优点"></a>优点</h2><ol>
<li>降低了目标和观察者之间的耦合关系，两者之间是抽象耦合关系</li>
<li>被观察者发送通知，所有注册的观察者都会收到消息，实现广播机制</li>
</ol>
<h2 id="缺点"><a href="#缺点" class="headerlink" title="缺点"></a>缺点</h2><ol>
<li>如果观察者非常多的话，那么所有的观察者收到被观察者发送的通知会耗时</li>
<li>如果被观察者有循环以来的话，那么被观察者发送通知会使观察者循环调用，会导致系统崩溃。</li>
</ol>
<h2 id="代码实现"><a href="#代码实现" class="headerlink" title="代码实现"></a>代码实现</h2><p>实现一个购房，抽奖摇号，摇号完成后，将消息分别通过短信发送给用户，和记录到MQ中。<br>抽奖摇号：被观察者<br>消息发送记录： 观察者</p>
<ol>
<li><p>相关实现类（实现的辅助类）</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><code class="hljs python"><span class="hljs-keyword">import</span> abc<br><span class="hljs-keyword">import</span> random<br><span class="hljs-keyword">import</span> datetime<br><br><br><span class="hljs-keyword">class</span> <span class="hljs-title class_">LotteryResult</span>:<br>    <span class="hljs-comment"># 用户抽奖结果对象</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">__init__</span>(<span class="hljs-params">self, uid, msg, dateTime</span>) -&gt; <span class="hljs-literal">None</span>:<br>        self.uid = uid<br>        self.msg = msg<br>        self.dateTime = dateTime<br><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">getUid</span>(<span class="hljs-params">self</span>):<br>        <span class="hljs-keyword">return</span> self.uid<br><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">getMsg</span>(<span class="hljs-params">self</span>):<br>        <span class="hljs-keyword">return</span> self.msg<br><br><br><span class="hljs-keyword">class</span> <span class="hljs-title class_">DrawHouseService</span>:<br>    <span class="hljs-comment"># 摇号操作</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">lots</span>(<span class="hljs-params">uid</span>):<br>        <span class="hljs-keyword">try</span>:<br>            <span class="hljs-keyword">if</span> <span class="hljs-built_in">int</span>(uid) % <span class="hljs-number">2</span> == <span class="hljs-number">0</span>:<br>                <span class="hljs-keyword">return</span> <span class="hljs-string">f&quot;恭喜id为<span class="hljs-subst">&#123;uid&#125;</span>,中签&quot;</span><br>            <span class="hljs-keyword">else</span>:<br>                <span class="hljs-keyword">return</span> <span class="hljs-string">f&quot;很遗憾id为<span class="hljs-subst">&#123;uid&#125;</span>,没有中签&quot;</span><br>        <span class="hljs-keyword">except</span> Exception <span class="hljs-keyword">as</span> e:<br>            <span class="hljs-keyword">return</span> <span class="hljs-string">f&quot;很遗憾id为<span class="hljs-subst">&#123;uid&#125;</span>,没有中签&quot;</span><br></code></pre></td></tr></table></figure></li>
<li><p>观察者管理方法（非必须）</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br></pre></td><td class="code"><pre><code class="hljs python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">EventManager</span>(metaclass=abc.ABCMeta):<br>    <span class="hljs-string">&quot;&quot;&quot;管理者接口</span><br><span class="hljs-string"></span><br><span class="hljs-string">    Args:</span><br><span class="hljs-string">        metaclass (_type_, optional): _description_. Defaults to abc.ABCMeta.</span><br><span class="hljs-string">    &quot;&quot;&quot;</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">__init__</span>(<span class="hljs-params">self</span>) -&gt; <span class="hljs-literal">None</span>:<br>        <span class="hljs-comment"># 监听器集合</span><br>        self.__listeners = []<br>    <br><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">subscribe</span>(<span class="hljs-params">self, listener</span>):<br>        <span class="hljs-string">&quot;&quot;&quot;订阅</span><br><span class="hljs-string"></span><br><span class="hljs-string">        Args:</span><br><span class="hljs-string">            listener (_type_): 监听对象</span><br><span class="hljs-string">        &quot;&quot;&quot;</span><br>        self.__listeners.append(listener)<br><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">unsubscribe</span>(<span class="hljs-params">self, listener</span>):<br>        <span class="hljs-string">&quot;&quot;&quot;取消订阅</span><br><span class="hljs-string"></span><br><span class="hljs-string">        Args:</span><br><span class="hljs-string">            listener (_type_): _description_</span><br><span class="hljs-string">        &quot;&quot;&quot;</span><br>        self.__listeners.remove(listener)<br><br>    <br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">notice</span>(<span class="hljs-params">self, result: LotteryResult</span>):<br>        <span class="hljs-string">&quot;&quot;&quot;通知</span><br><span class="hljs-string">        Args:</span><br><span class="hljs-string">            result (LotteryResult): 摇号结果</span><br><span class="hljs-string">        &quot;&quot;&quot;</span><br>        <span class="hljs-keyword">for</span> item <span class="hljs-keyword">in</span> self.__listeners:<br>            item.doEvent(result=result)<br></code></pre></td></tr></table></figure></li>
<li><p>抽象被观察者</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><code class="hljs python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">SubjectService</span>(metaclass=abc.ABCMeta):<br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">__init__</span>(<span class="hljs-params">self</span>) -&gt; <span class="hljs-literal">None</span>:<br>        self.eventManage = EventManager()<br>        <span class="hljs-comment"># 订阅</span><br>        self.eventManage.subscribe(MessageEventListener)  <span class="hljs-comment"># 短信</span><br>        self.eventManage.subscribe(MQEventListener)  <span class="hljs-comment"># MQ</span><br><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">lotteryAndMsg</span>(<span class="hljs-params">self, uid: <span class="hljs-built_in">str</span></span>):<br>        <span class="hljs-string">&quot;&quot;&quot;发送通知</span><br><span class="hljs-string">        Args:</span><br><span class="hljs-string">            Stringuid (_type_): _description_</span><br><span class="hljs-string">        &quot;&quot;&quot;</span><br>        lotteryResult = self.lottery(uid=uid)<br>        self.eventManage.notice(lotteryResult)<br><br><span class="hljs-meta">    @abc.abstractclassmethod</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">lottery</span>(<span class="hljs-params">self, uid: <span class="hljs-built_in">str</span></span>)-&gt;LotteryResult:<br>        <span class="hljs-comment"># 开奖</span><br>        <span class="hljs-keyword">pass</span><br></code></pre></td></tr></table></figure></li>
<li><p>具体被观察者</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><code class="hljs python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">LotteryService</span>(<span class="hljs-title class_ inherited__">SubjectService</span>):<br>    <span class="hljs-comment"># 具体被观察者</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">lottery</span>(<span class="hljs-params">self, uid: <span class="hljs-built_in">str</span></span>) -&gt; LotteryResult:<br>        <span class="hljs-comment"># 摇号</span><br>        result = DrawHouseService.lots(uid=uid)<br>        <span class="hljs-keyword">return</span> LotteryResult(uid=uid, msg=result, dateTime=datetime.datetime.now())<br></code></pre></td></tr></table></figure></li>
<li><p>抽象观察者</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><code class="hljs python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">EventListener</span>(abc.ABCMeta):<br>    <span class="hljs-comment"># 抽象观察者</span><br><span class="hljs-meta">    @abc.abstractmethod</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">doEvent</span>(<span class="hljs-params">result: LotteryResult</span>):<br>        <span class="hljs-string">&quot;&quot;&quot;事件处理</span><br><span class="hljs-string"></span><br><span class="hljs-string">        Args:</span><br><span class="hljs-string">            slef (_type_): _description_</span><br><span class="hljs-string">            result (LotteryResult): 处理结果</span><br><span class="hljs-string">        &quot;&quot;&quot;</span><br>        <span class="hljs-keyword">pass</span><br></code></pre></td></tr></table></figure></li>
<li><p>具体观察者</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><code class="hljs python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">MessageEventListener</span>(<span class="hljs-title class_ inherited__">EventListener</span>):<br>    <span class="hljs-comment"># 具体观察者(发送短信)</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">doEvent</span>(<span class="hljs-params">result: LotteryResult</span>):<br>        <span class="hljs-built_in">print</span>(<span class="hljs-string">f&quot;发送短信通知，用户ID: <span class="hljs-subst">&#123;result.getUid()&#125;</span>, 您的摇号结果为: <span class="hljs-subst">&#123;result.getMsg()&#125;</span>&quot;</span>)<br><br><br><span class="hljs-keyword">class</span> <span class="hljs-title class_">MQEventListener</span>(<span class="hljs-title class_ inherited__">EventListener</span>):<br>    <span class="hljs-comment"># 具体观察者（记录数据到MQ）</span><br>    <span class="hljs-keyword">def</span> <span class="hljs-title function_">doEvent</span>(<span class="hljs-params">result: LotteryResult</span>):<br>        <span class="hljs-built_in">print</span>(<span class="hljs-string">f&quot;记录用户的摇号结果(MQ)，用户ID: <span class="hljs-subst">&#123;result.getUid()&#125;</span>, 摇号结果为: <span class="hljs-subst">&#123;result.getMsg()&#125;</span>&quot;</span>)<br><br></code></pre></td></tr></table></figure></li>
<li><p>主方法</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><code class="hljs python"><span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">&quot;__main__&quot;</span>:<br>    lotterServer = LotteryService()<br>    lotterResult = lotterServer.lotteryAndMsg(uid=<span class="hljs-string">&quot;123&quot;</span>)<br><br></code></pre></td></tr></table></figure></li>
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